1. Field of the Invention
This invention pertains to sorting machines that separate substandard fungible items from standard items, the items flowing through the machine in large volumes at high rates of speed.
2. Description of the Prior Art
A typical sorting machine of the type envisioned for application of the present invention is a high speed sorting machine typically used for sorting fungible products in the food industry or otherwise. For example, individual rice grains are caused to flow by gravity feed down a steep channel to be sorted in such a machine to separate "substandard" grains from standard grains. The term "substandard" can apply to a dark grain that has no useful purpose, but the term can also apply to a grain of different length or other quality that is perfectly acceptable in the abstract, but is not within the standard limits of quality established for acceptable standard products for a particular sorting.
Although products of the type just described can theoretically be sorted by weight, mechanical measurement size or the like, perhaps the most commonly employed sorting mechanism used in today's machines employ optical sensors. Such sensors include one or more photodetectors, such as photodiodes, that are sensitive not only to black, white and shades of gray differences, but also to subtle variations in color hues. Also, such sensors, including the entire sensor combination of parts, are also capable of discriminating against different sizes of products. All of the machines of the general class fitting the above description have in common a protective, light admitting window for the sensor or sensors to protect these sensors from contamination. In some cases, the "window" may only be the sensor element covering, but in many cases it is the common housing enclosing a plurality of sensors that are spaced about an opening through which is directed the flow of product to be sorted.
Such machines also include an ejector mechanism located downstream from the sensor or sensors and actuated by an electrical signal originating from sensor detection. When a substandard product is detected, an electrical actuating signal is produced and the ejector is actuated just as the substandard product and the mechanism are in alignment. Therefore, there is a delay between detection and ejection, but it is ever so slight because the further the ejector is from the detector, the more the substandard product can "escape" by being diverted or hit by other products in the product flow or even by velocity variations caused by friction in the channel depending on the duration of contact with the flow channel or slide as the products tumble along. Therefore, the ejector is normally located as close as possible to the sensor or sensors, ideally being just downstream therefrom and closely adjacent thereto.
The ejector mechanism can be mechanical, but for small fungible products it is almost universally a compressed air ejector. That is, when the substandard product arrives opposite the ejector, the ejector emits a sharp expulsion or jet blast of air that kicks the substandard product from the stream. Typically, the ejector includes an elongated nozzle that has a very narrow opening, at least in the dimension parallel to product flow. The opening is typically slotted or elongated, however, transverse to the flow direction.
Each time the ejector expels a jet or blast of air, not only is the substandard product ejected from the main product stream, the surface of that product and other products that are also contacted by the blast are "dusted". That is, minute loose surface flakes are blown off or apart from the products themselves, these loose surface flakes settling wherever they are blown. These flakes are sometimes referred to collectively as "dust". Most of these dust flakes or particles are harmlessly blown out of the main product flow with the ejected product, but many of these flakes are scattered in various other directions. The ones that cause the most mischief are the ones that settle on the window or windows of the optical sensors, previously described. This is because over a period of time there is a build up of these dust flakes that cause the window or windows to become more and more opaque to the passage of light, which interferes with the sensitivity of discrimination detection necessary for proper sorting operation. When there is excessive build-up, the machine has to be cut off and the window or windows cleaned before the machine is ready to properly operate again. Obviously, it is desirable to minimize the amount of this down time.
Therefore, it is a feature of the present invention to provide an improved sorting machine including air ejection separation of substandard products from a flow of fungible products wherein the ejection mechanism does not rapidly coat the window of a nearby optical sensor with product dust.
It is another feature of the present invention to provide an improved air ejector for separating substandard products from a flow of fungible products passing through a sorting machine, the improved air ejector developing a pressure differential in the air blast therefrom to minimize the number of dust particles that disperse to accumulate on a nearby sensor window.